1. Field of the Invention
The present invention relates to a device and a method for cutting and grinding a doughnut shaped substrate of a hard but brittle material such as plate glass etc.
2. Description of the related art
As materials of disc substrates used for high density information media, conventionally metals such as aluminium etc. and non-metallic materials such as ceramic, plastic are used, and recently, glass material has come to be used greatly with the reason that it is excellent in flatness (degree of planarity).
As a disc substrate, in general, a doughnut shaped substrate having a circular hole at its central portion has been widely used. However, in the case of a doughnut shaped substrate of glass just after its having been cut, many minute irregularities generated in the course of cutting and grinding of the substrate remain at the inner circumference and the outer periphery of the substrate, so that finishing work and chamfering work must be carried out for removing the irregularities and improving strength of the substrate.
Because of the aforedescribed reasons, conventionally, for example, as disclosed in Japanese utility model laid-open publication No. 63-201048 and Japanese utility model laid-open publication No. 63-64460, glass is cut to a doughnut shape and the doughnut shape substrate is suctionedly secured on a vaccum suctioning table. Then, the doughnut shape substrate is accommodated in an inner circumference and outer periphery cutting and grinding device. In the device both the inner circumference and the outer periphery of the doughnut shape substrate are contacted with annular cavities formed respectively at the circumferential wall and the outer periphery of a core, and by rotating the device and the vacuum suctioning table respectively and give horizontal movement between the device and the substrate to cut and grind the inner circumference and the outer periphery of the doughnut shape substrate.
However, in the afore-described conventional method for manufacturing a doughnut shape substrate, at least two steps are indispensably necessary. That is, one of them is a work to cut a glass plate to a doughnut shape, and the other is to perform finishing and chamfering work of the peripheral surface.
Therefore, one place for cutting down a doughnut shape plate(s) from a glass plate and the other is an operating place at which work for finishing and chamfering the inner circumference and the outer periphery of the doughnut shape plate are carried out. Thus, wide space is needed. Further, after the doughnut shape plate is cut down from the glass plate, when the doughnut plate is placed on the vacuum suctioning table on which the finishing and chamfering work is performed, aligning their axes is very complicated and if they do not coincide precision of the doughnut shape substrate is lowered.